Luminescence excitation in an irradiated solid: type IIb diamond

Excitation spectroscopy is a useful technique for unrevealing absorption spectra of defects in solids. However, excitation spectra obtained using an absorbing sample will suffer distortion through limitation of the excitation intensity in the body of the sample. We use a simple analytical description of light absorption in solids to obtain corrected excitation spectra of the dominant luminescent defects in electron-irradiated type IIb diamond. It is thereby possible to make a clear separation of absorption due to different species of defects in this material. We obtain the first reliable estimates of band-shape parameters (moments of the transition probability) for the phonon-assisted sideband of the 'GRI' zero phonon line, and we obtain further experimental evidence concerning the nature of the 'GR2-8' lines, from the excitation spectrum. In addition, we establish by direct means the common origin of a number of absorption bands found in annealed material. The so-called 'TR bands' are reassigned to the di-interstitial on the basis of our identification of a localised phonon 'signature'. The absorption spectrum of irradiated type IIb diamond can now be understood as a superposition of absorptions due to a small number of distinct defect species.